Glucolipid-enriched extract of Osmanthus fragrans flowers inhibits LPS-induced inflammation

Osmanthus fragrans Lour., also known as sweet olive, is a plant native to East Asia. Its flowers have been traditionally used to treat various diseases accompanied by inflammation and pain [1]. The aim of this study was to investigate their anti-inflammatory properties and active constituents. n-Hexane and CH2Cl2 extracts of Osmanthus fragrans flowers at concentrations of 20 µg/ml inhibited COX-2 mRNA expression by 48.8±4.2 and 46.2±5.3%, respectively. Starting from these extracts, activity-guided fractionation led to a glucolipid-enriched fraction, mainly composed of digalactosyl-diacylglycerols (DGDGs) and monogalactosyl-monoacyl-glycerols (MGMGs). In total, four MGMGs and six DGDGs were identified by means of LC-MS. The corresponding fraction was not only able to inhibit COX-2 mRNA expression in LPS-stimulated PMA-derived macrophages, but also suppressed LPS-induced IL-8 secretion and E-selectin expression in endothelial cells. The active fraction inhibited proinflammatory effects of LPS, but did not suppress action of TNF-α and IL-1β, thus pointing to a selective inhibition of the TLR4 receptor.